Even now, according to experts PEOPLE spoke to on the anniversary of Cunanan’s slayings, it’s still not clear what drove the 27-year-old hustler to travel across the country killing people he knew and others he did not.

“Investigators really didn’t have what they felt was a concrete motive,” says John Kelly, a criminal profiler and serial killer expert.

Versace, shot early on July 15, 1997, outside his Miami Beach, Florida, mansion, was the last of Cunanan’s victims. His murder was “quick,” says crime scene investigations technician Berta Valdez, who helped process the scene. “Almost execution-style. One, two shots, and he was killed almost instantly.”

“The other victims,” Valdez adds, “weren’t so lucky.”

• For more on Versace’s shocking murder and Cunanan’s deadly spree, subscribe now to PEOPLE or pick up this week’s issue, on newsstands Friday.

Jeffrey Trail

AP Photos/File

David Madson

AP Photos/File

Cunanan’s killings — which lacked a consistent m.o. or clear cause — began in Minneapolis in late April of 1997, when he murdered close friend Jeffrey Trail, a 28-year-old former U.S. Naval Officer, with a claw hammer, before shooting 33-year-old architect David Madson, an ex-lover, with a gun belonging to Trail.

More than a week later, on May 4, 1997, Cunanan tortured and killed millionaire Chicago real estate magnate Lee Miglin, 72, whose relationship to Cunanan, if any, is still unclear.

From there Cunanan traveled to an out-of-the-way cemetery in Pennsville, New Jersey, where he shot caretaker William Reese, 45, before stealing Reese’s red Chevy pickup truck for the drive to Miami.

Already the subject of a nationwide manhunt, Cunanan remained in hiding until he shot Versace. He killed himself a few days later, on a houseboat, as authorities closed in.

Lee Miglin

AP Photos/File

Gianni Versace (left) and Andrew Cunanan

George Rose/Getty; AP

“Suicide is the ultimate act of control and power,” Kelly explains. “Ending his own life was the icing on the cake. He accomplished what he wanted to accomplish.”

Cunanan “grew up feeling powerless and being kind of out of control,” Kelly says. “He wanted to be in the spotlight. Fame brings power.”

While the FBI never believed there was a relationship between Versace and Cunanan, or that the former even knew the latter’s name, Kelly thinks the motive in that final murder was “pretty clear.”

“I think he [Cunanan] was looking for fame,” Kelly says. “His goal was to kill a famous man. He did, and he became infamous.”

‘I Still Don’t Understand’

Now 32, Troy Reese was just 12 years old when Cunanan killed his dad, William, in the basement of the caretaker’s cottage at the New Jersey cemetery where he worked.

William worked at Finn’s Point National Cemetery — “and that cemetery is all the way back in the woods, it’s in no man’s land,” Troy says.

“So somehow,” he says, “the guy found my dad’s cemetery where he was working.”

William Reese

AP Photos/File

Two decades later, William’s death remains “as painful today as it was then,” his son says. “My dad trusted people, like I do, and took him in the basement of the caretaker’s house where Cunanan executed him.”

“He was their sun,” says friend Hal Rubenstein, a fashion writer and consultant. “He was making everything move and suddenly he got ripped away. It was tailspin time for everybody.”

Adds another family friend, “I think it’s fair to say that the family really didn’t have time or the opportunity to grieve the way you and I would grieve at the awful loss of somebody.”

“For several years after his murder, they were under the microscope of the entire world,” the friend says. “So when that slowly started to get back to normal and the spotlight kind of started to go to its normal level of glow on the family and the business, that’s when they really first started to grieve.”